In recent years, various forms and configurations of communication systems have been designed and developed for use in many applications and industries. Conventional communication systems include one or more reader devices in limited-range communication with one or more communication devices. A reader device is typically configured to periodically, intermittently or continuously broadcast an interrogating signal in one or more directions in and around its vicinity to one or more communication devices that are within communication range.
Various configurations of communication systems are in use today, such as those having a stationary reader device and at least one portable communication device, a portable reader device and at least one stationary communication device, and a portable reader device and at least one portable communication device. In applications requiring one or more portable communication devices and/or reader devices, such as access key applications for gaining access to a secured facility, there are several important and inter-related factors that are considered, including the achievable communication range between the communication device and the reader device, the size of the portable communication device, and the duration of use of the portable communication device before maintenance, such as the operational duration of the portable communication device before its battery must be replaced. In regards to communication range, it is typically desirous that the distance be as large as possible. In achieving larger communication ranges, however, it is generally known that a communication device will require, among other things, a sufficiently larger source of stored energy, such as a battery, to generate a stronger response signal. The inherent trade-offs with having larger energy sources pertain to the inherently increased size and shortened useable duration of the communication device. Specifically, in having a larger energy source, the size of the communication device will correspondingly become larger as a result. Furthermore, the useable duration before maintenance of the communication device will generally become shortened due to the increase in power consumption and the need for replacing or recharging the energy source, such as a battery.
A conventional communication device having one or more external energy sources, such as a battery, is generally referred to as an active device. Recent advances in communication systems have resulted in the widespread use of passive communication devices, that is, those which do not utilize an external energy source, such as a battery. In general, a passive communication device only becomes activated to process and transmit a response signal upon coming into sufficient communication range of a reader device. Upon coming into communication range of a reader device and receiving a broadcasted interrogating signal from the reader device, the communication device converts the signal into energy. This energy is then stored and made available for processing and generating a response signal. In this regard, the amount of energy that is converted and stored will depend directly on the received signal strength of the broadcasted interrogating signal, which is directly related to the distance between the communication device and the reader device. Because passive communication devices do not utilize an external energy source, such as a battery, their size can be substantially smaller than active communication devices. Furthermore, passive communication devices do not suffer from the same problem of having a limited duration of use before maintenance since there are no batteries to replace. However, because passive communication devices can only convert and store a small amount of energy, passive communication devices will inherently have much shorter communication ranges when compared with active communication devices.
In general, conventional communication systems are limited by problems pertaining to increasing the communication range and improving the reliability of communications at extreme communication range distances of the communication system. For instance, irrespective of whether the communication system is active, passive or a combination thereof, a communication device may be within receiving range of a weak interrogating signal from a reader device but still not be within communicable range. This may be due to, among other reasons, the weakness of the received broadcasted interrogating signal at the communication device and/or the weakness of the received response signal at the reader device. In this respect, such problems typically occur slightly within, at or slightly beyond the maximum communication range distances designed for the communication system.
Presently, there are several known ways to improve the communication range of a communication system. For example, increasing of the strength of a transmitted interrogating signal can effectively increase the communication range and storable energy in communication devices. However, such improvements to the reader device are expensive and typically require corresponding improvements to the antenna and/or size of the energy source of the communication device, which typically results in an increase in size and reduction in duration of use of the communication device, and an increase in the overall cost and complexity of the communication system. Furthermore, such improvements have not been able to improve the reliability of communication at extreme communication ranges. As another example, improving the antenna of the reader device and/or communication device to a higher quality, lower loss and/or larger size antenna may also increase the communication range of the system. However, such improvements will not only increase the size and reduce the duration of use before maintenance of the communication device, but also substantially increase the overall cost and complexity of the communication system. Furthermore, such improvements have not been able to improve the reliability of communication at extreme communication ranges. As another example, reducing the power consumption of the processor of the communication device and/or adding an external energy source, such as a battery, will effectively improve the communication range. However, such improvements will typically result in an increase in size and/or reduction in duration of use before maintenance of the communication device, and also increase in the overall cost and complexity of the communication system. Furthermore, such improvements have not been able to improve the reliability of communication at extreme communication ranges. An example comparison of a modulated response signal (A) generated using any one or more of these known communication range improvement methods and a modulated response signal (B) not using one of these known improvement methods is illustrated in FIG. 1. In this regard, despite improving communication range, all of these existing solutions share common associated problems pertaining to increased size, reduction of duration of use before maintenance and/or substantial increase in overall costs and complexity of the communication system. Furthermore, all of these existing solutions fail to improve the reliability of communication at extreme communication ranges of the communication system.